1. Field of the Invention
The present invention relates to a method of creating photo mask data for use in manufacture of a photo mask, a method of manufacturing a photo mask, including a manufacturing and inspecting a photo mask by using the photo mask data, and a method of manufacturing a semiconductor device.
2. Description of the Related Art
Along with reduction of size of semiconductor devices, a pattern of a photo mask used for manufacturing a semiconductor devices is becoming finer and finer. As the pattern becomes finer, it is more difficult to detect small defects formed on the photo mask correctly.
As one of apparatus for inspecting shape defects on a photo mask, shape defect inspection of a die-to-database comparison system is known (Jpn. Pat. Appln. KOKAI Publication No. 8-87101). One of causes of decline of precision inspection of this shape defect inspection is false detection of a normal fine pattern as defect. Such defect is called false defect.
If a number of false defects are detected, inspection is stopped. When inspection stops, it is attempted to suppress detection of false defects. Specifically, the inspection sensitivity is adjusted or the inspection sensitivity is lowered. However, if the inspection sensitivity is changed, inspection of high precision is not expected.
As the pattern becomes further finer, it is more difficult to finish the fine pattern in a desired pattern shape on the wafer. The reason is that pattern distortion or line width dimension variation due to optical proximity effect cannot be ignored.
To prevent pattern distortion or line width dimension variation due to optical proximity effect, a technology known as optical proximity correction (OPC) is needed. In the existing defect inspection apparatus, however, it is hard to inspect a photo mask including a fine pattern such as an OPC pattern.
In shape defect inspection for a high precision mask, reflection type inspection is attempted for the purpose of enhancing the inspection sensitivity in addition to conventional transmission type inspection.
In the case of reflection type inspection on a halftone (HT) mask, a data image of a pattern (a mask data image) formed on a photo mask is generated on the basis of intensity of two lights, that is, light reflected from a glass portion of the photo mask, and light reflected from a HT film. The mask data image and the inspection data image are compared with each other, and it is detected as defect formed on the photo mask where the difference of two images exceeds a specified value.
The HT mask has a region whose transmissivity changes in three steps (three-gradation region). The three-gradation region includes a tritone portion including a glass portion, a HT film portion, and a light shielding film portion. The three-gradation region is locally present in peripheral parts of an inspection region or the like. The HT mask further includes a boundary between the three-gradation region and the light shielding film portion.
An example of a pattern including such a boundary between the three-gradation region and the light shielding film portion is shown in FIG. 15A. In FIG. 15A, reference numeral 81 is a quartz substrate (Qz), 82 is a halftone film (HT) formed on a region in part of the quartz substrate 81, 83 is a Cr film as a light shielding film formed on a region in part of the halftone film 82, and 84 is a boundary between the three-gradation region and the light shielding film.
The transmissivity of the halftone film 82 is 30%, for example, when a light source is ArF. FIG. 15B shows an optical image (transmission) in arrow view A-A in FIG. 15A.
The boundary 84 between the three-gradation region and the light shielding film is detected as noise 85 as indicated by a reflection profile in FIG. 15C in reflection type inspection under an ordinary inspection condition.
In transmission type inspection, the boundary 84 between the three-gradation region and the light shielding film is not detected as noise as shown in FIG. 15D.
In reflection type inspection, since the boundary 84 between the three-gradation region and the light shielding film is detected as false defect, inspection may be stopped. To suppress detection of false defect, the inspection sensitivity must be lowered. However, when the inspection sensitivity is lowered, precise inspection is not expected, and inspection throughput is lowered.
In some masks, only a specific region of the entire mask is inspected. However, in such a case, an area to be inspected must be preliminarily specified by input of coordinates, which involves a risk of human error of input by an operator.